1. Field of the Invention
The present invention relates generally to a weft yarn sensor for a weaving loom which senses the proper picking or insertion of the weft yarn into a predetermined position during the operation of the weaving loom and particularly to a weft yarn sensor for use in a fluid jet shuttleless weaving loom in which a weft yarn is inserted via a jet flow of fluid such as air which entrains the weft yarn and is guided or passed into the predetermined position through apertures formed in guiding members of an air guiding comb for preventing the diffusion of the fluid flow and a reduction in or a loss of the impetus of the fluid flow.
2. Description of the Prior Art
As is well known in the art, a conventional weft yarn sensor of this type includes a sensor body 10 as shown in FIG. 1 of the accompanying drawings which is located on a side of the air guiding comb near the weft yarn catching means and is swingably supported together with the air guiding comb and the reed. The sensor body 10 has two arms 11 and 12 defining an aperture 13 therebetween and formed so as to define a gap 14 between the ends thereof. The weft yarn 15 is passed through the apertures of the guiding members, and subsequently passed through the aperture 13 of the sensor body 10, then passed through gaps formed in the guiding members and the gap 14 of the sensor body 10 outside the apertures of the guiding members and the aperture 13 in the midst of the movement of the reed into its beat-up position. The arm 11 is provided with light projecting means 16 formed of light conductive means e.g. optical fibers which transmits light from a light source to the end of the arm 11 and projects the light to the end of the arm 12. The arm 12 is provided with light receiving means 17 such as, for example, photoelectric cell which receives the light projected from the light projecting means 16 to the end of the arm 12. The light projecting and receiving means 16 and 17 both are in the form of a circle at the ends of the arms 11 and 12.
When the weft yarn 15 is passed through the gap 14 outside the aperture 13, it intercepts the light projected from the light conductive means 16 to vary the quantity of light received by the light receiving means 17. This causes a change in the output of a light receiving device such as phototransistor connected to the photoelectric cell to sense that the weft yarn 15 has been properly inserted into the predetermined position. However, in the conventional weft yarn sensor, since only one beam is intercepted by the weft yarn 15 passed through the gap 14, a change in the quantity of light intercepted by the weft yarn 15 is extremely small and the time when the weft yarn 15 intercepts the beam is several milliseconds and accordingly fairly short. Thus, a change in the output of the light receiving device can not be sufficiently sensed by a sensing circuit and accordingly the conventional weft yarn sensor has been unable to surely and easily sense whether a weft yarn has been satisfactorily inserted into the predetermined position or not during loom operation.
Furthermore, when a fly fluff is sticked to the light projecting and/or receiving means 16 and/or 17 at the ends of the arms 11 and 12, since the fly fluff is in the form of a ball or a disk, it intercepts the light projected to the light receiving means 17 so that the conventional weft yarn sensor has malfunctioned as if the weft yarn has been properly inserted even through the weft yarn has in fact not been properly inserted.